This invention relates to a flowmeter for monitoring the flow of liquid in a sewerage system, and more specifically relates to a novel adapter structure for permitting connection of a flowmeter to a sewer pipe, as by connection to the open end or discharge end of the influent sewer pipe within a manhole, and to permit the use of ultrasonic flow measurement techniques even though the sewer pipe is not normally completely filled.
The desirability of measuring flow in a sewerage system is well known and systems for making this measurement are shown, for example, in U.S. Pat. No. 3,633,417, entitled REMOVABLE SEWER CONDUIT FLOWMETER, dated Jan. 11, 1972. Such systems have recognized the need for making the flow rate measurement in a completely filled pipe even though the sewerage pipe might be only partly filled. As shown in the above patent, the discharge from the open end of an influent pipe in a manhole is provided with an adapter structure having an upwardly disposed discharge end to insure that the adapter structure will always be filled with liquid. An impeller flowmeter is then placed within the adapter structure in order to provide a flow measurement which is related to the flow of fluid, whether sewerage or water, in the partially flled sewerage system leading into the manhole.
Arrangements of the prior art have required relatively complex flow control systems for insuring that liquid fills the top of the adapter system by providing gates and the like for damming the end of the pipe containing the measuring equipment.
The present invention provides, in one embodiment, a novel adapter tube construction which can be temporarily or permanently located within the manhole, with the measurement system being secured for operation through the activation of a jack-screw arrangement which is easily installed in the manhole to connect the flow monitor to the influent sewer pipe. A further feature of the invention enables the use of a plastic flow tube which has clamp-on flow monitoring transducers connected thereto, which tube is suitably inserted in the flow path of the sewer pipe. Thus, transducer arrangements and ultrasonic processing circuits of the type disclosed in either of U.S. Pat. Nos. 3,869,915 or 3,987,674, each in the name of Baumoel, can be used in connection with the present invention. The subject matter of each of the above patents in the name of Baumoel are incorporated herein by reference.
A futher important feature of the present invention is that the adapter tube may be made of a plastic material, so that it can be used in a highly reactive environment without danger of corrosion, and yet permits the use of ultrasonic measurement techniques. Thus, the plastic flow tube has a roughened outer periphery to prevent internal ultrasonic reflections from the interface between the outer surface of the tube and the surrounding environment. That is, when using ultrasonic flow measurement techniques (and if the measurement transducers are on the same side of the pipe axis), the portion of the ultrasonic beam used for the measurement is the portion which passes through the liquid, and is reflected from the interior pipe wall. However, and particularly if the pipe is made of plastic rather than metal, a substantial portion of the sound energy through the fluid in the pipe will enter the pipe wall. This energy will then be coherently internally reflected from the outer pipe wall, and can reenter the liquid through the inner pipe wall, and can interfere with the measurement.
In accordance with the invention, a suitable anticoherent reflection means is placed on the outer tube surface to break up the reflection from the surface to destroy its coherency with reflections from the inner pipe wall .